Exam II Pt. 5

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Exam II Pt. 5
2013-10-13 12:46:54
Required Reading

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  1. Tight Junctioins

                                                                  i.      a __ is composed of a layer of cells that adhere tightly to one another to form a __
                                                                ii.      why can’t solutes and ions move through by way of a paracellular pathway? à __
                                                              iii.      located at the very __end of the __ between __
    • simple epithelium
    • cellular sheet
    • tight junctions between neighboring epithelial cells
    • apical 
    • junctional complex
    • adjacent epithelial cells
  2.                                                               i.      adjoining membranes make contact at __, rather than being __

    1.      points of __ are sites where __ of two adjacent membranes meet within the extracellular space
                                                                ii.      tight junctions contain __ that run mostly __to one another and to the __ of the epithelium
    • intermittent points
    • fused over a large surface area
    • cell-cell contact
    • integral proteins
    • interconnected strands
    • parallel 
    • apical surface
  3. 1.      the strands correspond to paired rows of __
    a.      the integral proteins of TJs form __ that completely encircle the cell like a gasket and make contact with neighboring cells on all sidesà TJs serve as a __
    • aligned integral membranes
    • continuous fibrils 
    • barrier to the free diffusion of water and solutes from the extracellular compartment on one side of an epithelial sheet to that on the other side
  4.                                                               i.      TJs also serve as __that help maintain the c__ of epithelial cells by __ between the __ of the plasma membrane and its __
                                                                ii.      TJs also involved in __that regulate numerous cellular processes
    • fences 
    • polarized character
    • blocking diffusion of integral proteins
    • apical domain
    • lateral and basal domains
    • signaling pathways
  5.                                                               i.      not all TJs exhibit the same __properties
    1.      those with __ form better seals than junctions with only one or a couple of strands
    2.      some are permeable to specific ions or solutes to which other TJs are impermeable
    • permeability 
    • parallel strands
  6.                                                               i.      In 1998, it was thought that TJ strands were composed of a single protein, __
    1.      revealed that cultured cells lacking __still formed TJ strands
    a.      this led to discovery of __that form the major structural component of TJ strands
    • occludin x2
    • claudins
  7.                                                                                                                                       i.      __ and __ are present together within the linear fibrils of a TJ
    1.      at least 24 different __identified, and differences in the distribution of these proteins explain differences in TJ permeability
    a.      __ in kidney tubules and permeability to Mg2+
    • occludin and claudin
    • claudins 
    • claudin-16
  8. another important function of Tight Junctions
    • 1.      before it was though that impermeability of mammal skin to water was due to cornified layer of skin, but revealed that cells in outer layers of normal epidermis are connected by tight junctions
    • a.      animals lacking this had uncontrolled water loss
  9.                                                               i.      tight junctions also present between the __ that line capillary walls
    1.      form __, which prevents diffiusion from bloodstream to brain
    • endothelial cells
    • blood-brain barrier
  10. a.      Gap Junctions and Plasmodesmata
                                                                  i.      gap junctions are __
    1.      where plasma membranes of adjaenet cells __

    2.      instead, the cleft  between the cells is __by very __that are actually __ that pass through the __ and open into the __
    • sites between animal cells that are specialized for intercellular communication
    • come very close to one another without making direct contact
    • spanned 
    • fine strands 
    • molecular pipelines
    • adjoining plasma membranes
    • cytoplasm of the adjoining cells
  11. Gap Junctions                                                             
    simple molecular composition; they are composed entirely of an integral membrane protein called __
    1.      organized into __, called __, that completely span the membrane

    • connexin
    • multisubunit complexes
    • connexons
  12. Explain connexons.
    a.      each connexon is composed of six connexin subunits arranged in a ring around a central opening, or annulus, that is approx. 1.5 nm in diameter at the extracellular surface
  13.                                                               i.      during formation of gap junctions, the connexons in the plasma membranes of apposing cells do what?
    become tightly linked to one another through extensive noncovalent interactions of the extracellular domains of the connexin subunits
  14. 1.      once aligned, __in apposing plasma membranes form complete __ connecting the cytoplasm of one cell with the cytoplasm of its neighbor
    a.      large numbers of __become clustered in specific regions of the membrane, forming __ that can be seen in freeze fracture
    • connnexons 
    • intercellular channels
    • connexons 
    • gap-junction plaques
  15.                                                               i.      gap junctions are sites of __
    1.      existence of gap-junction intercellular communication is revealed through the passage of either ionic currents or low-moleculear weight dyes, such as fluorescence, from one cell to its neighbors
    a.      mammalian gap junctions allow diffusion of molecules having a molecular mass below 1000 daltons
    communication between the cytoplasms of adjacent cells
  16. a.      in contrast to the highly selective ion channels that connect a cell to the external medium, gap junction channels are __, but can be __
                                                                                                                                          i.      channel closure is probably triggered primarily by __of __subunits
                                                                                                                                        ii.      closer can also be triggered by changes in __ across the junction or abnormally high __
    • nonselective
    • gated
    • phosphorylation 
    • connexin 
    • voltage
    • cytosolic Ca2+ concentrations
  17.                                                               i.      gap junctions are involved in stimulation of a __
    cardiac or smooth muscle
  18. Cardiac stimulation by gap junctions:
    1. contraction of the mammalian heart is stimulated by an __ generated in a small region of specialized heart muscle called the __, which acts as the heart’s __
    • electrical impulse
    • sinoatrial node
    • pacemaker
  19. Cardiac stimulation by gap junctions:
    2. the impulse spreads rapidly as a current of ions flows through __ from one __ cel to its neighbors, causing the cells to contract in __
    • gap junctions
    • cardiac muscle
    • synchrony
  20. Smooth muscle stimulation:
    3. similarly, the flow of ions through __ that interconnect __ in the wall of the esophagus or intestine leads to the generation of coordinated __ that move down the length of the wall
    • gap junctions
    • smooth muscle cells
    • peristaltic waves
  21.                                                               i.      gap junctions can put many tissues cells into __
    1.      important since a lot of highly active regulatory substances like __are small enough to fit through __--> __ have potential to integrate the activities of individual cells of a tissue into a __
    • intimate cytoplasmic contact
    • cAMP 
    • gap-junction x2

    functional unit
  22.                                                               i.      gap junctions also allow cells to cooperate metabolically by sharing key __, such as ATP, sugar phosphates, amino acids, and many __, which are small enough to pass through these intercellular channels
    • metabolites
    • coenzymes
  23. 1.      __ (Cx), the proteins of which gap junctions are constructed, are members of  a __

    a.      nearly __different __with distinct tissue-specific distributions
    • connexins
    • multigene family
    • 20 
    • connexins
  24. a.      __composed of different __ exhibit marked differences in __, __, and __
                                                                                                                                          i.      in some cases, __in neighboring cells that are composed of different __ are able to doct and form functional channels, whereas in other cases, they are not
    • connexons 
    • connexins
    • conductance
    • permeability
    • regulation
    • connexons 
    • connexins
  25. 1.      these compatibility differences may play important roles in either __ or __ __ __between different types of cells in an organ
    • promoting or preventing
    • communication
  26.                                                               i.      a new type of communication system discovered consisting of thin, highly elongated tubules capable of conducting __ (3) __from one cell to another over long  distances and transmit infectious viral particles and prions between cells
    1.      to date, these __ have been studied primarily in cultured cells
    • cell-surface proteins, cytoplasmic vesicles, and calcium signals 
    • tunneling nanotubes
  27. a.      Plasmodesmata
                                                                  i.      plants, due to cell wall, are connected by these, which are __

    1.      lined by __ and usually contain a __, the __, derived from the __of the two derived from the __ of the two cells
    • cytoplasmic channels that pass through the cell walls of adjacent cells
    • plasma membrane
    • dense central structure
    • desmotubule
    • smooth endoplasmic reticulum 
    • smooth ER
  28.                                                               i.      like __, they serve as sites of __, as substances pass through the __surrounding the __
                                                                ii.      allow much larger molecules to pass between cells, since they __

    • gap junctions
    • cell-to-cell communication
    • annulus 
    • desmotubule
    • dilate
  29. 1.      discovery: vruses encoded a __ that interacted with the wall of the __and increased the __of the pore
    a.      plant cells produce their own __that regulate the flow of proteins and RNAs from cell to cell
                                                                                                                                          i.      some get into plant and integrate activities
    • movement protein
    • plasmodesmata 
    • diameter 
    • movement proteins